Aggression is a ubiquitous behavior important in social interactions such as the establishment of territory, access to food source, and mating success. Excessive aggression is also one symptom of some neurodegenerative disorders. Aminergic transmitters such as serotonin, dopamine, and norepinephrine (or its invertebrate homologue, octopamine) are one well-established category of neurotransmitter that play a role in aggression. In vertebrates, important roles for two families of peptides in aggression also have been established (AVP and GnRH peptide families) but these have been less well studied in invertebrate systems. With the use of behavioral analysis, immunocytochemistry to examine the co-localization of peptides and amines, and the GAL4/UAS system to genetically manipulate neuropeptide release, the role of peptides in aggression will be examined in a Drosophila model, which allows for the rigorous quantification of fighting behavior. The aims proposed here explore the possibility: (I) that neuropeptides are co-expressed with biogenic amines in the D. melanogaster nervous system; and (II) that the co-expressed peptides or peptides that interact with amine neurons play a role in regulating aggression.